Interesting RK8E fault

On Dec 8, 2018, at 8:50 PM, Josh Dersch via cctalk <

On Sat, Dec 8, 2018 at 7:24 PM Paul Anderson via cctalk < cctalk at classiccmp.org> wrote: I connected the drive I normally use with my 11/40 to the 8/e for testing to help narrow down where the fault was. I used a 16-sector pack in all cases.

> > On Sat, Dec 8, 2018 at 8:54 AM Bill Degnan via cctalk < > cctalk at classiccmp.org> > wrote: > >> On Sat, Dec 8, 2018, 1:02 AM Josh Dersch via cctalk < > cctalk at classiccmp.org >> wrote: >> >>> On Fri, Dec 7, 2018 at 9:58 PM Josh Dersch <derschjo at gmail.com>

>>> >>>> Hi all -- >>>> >>>> Finally got all the parts together (and my act together) to actually >> get >>>> an RK05 lashed up to my PDP-8/e -- only took a decade or so :). I >> fixed >>> a >>>> few problems with the RK05 and it appears to be behaving very nicely. >>>> >>>> The RK8E controller is mostly working properly but fails > interestingly >>>> when running the formatter, and during the exerciser -- on cylinder > 128 >>> and >>>> 192 and very infrequently on cylinder 64 it will get a cylinder >> mismatch >>>> when doing the seek. When running the formatter during the >> verification >>>> pass, on cyls 64 and 128 if I retry the read it'll continue without >>> issues, >>>> but it's never successful on a retry on cylinder 192. I tried > hooking >> it >>>> to the RK05 in my 11/40 and it exhibits the same behavior, so I'm >>> guessing >>>> the drive isn't at fault. And the error is consistent across packs > (of >>>> which I have only two). >>>> >>>> Apart from that fault the drive and controller seem to work fine -- I >>>> wrote out an OS/8 pack with Adventure on it (or at least the first > 191 >>>> cylinders of it) and it works without issue. >>>> >>>> Reading the RK8E service docs and schematics, the cylinder address >>> compare >>>> is done by reusing the CRC buffer, so I suspect the issue is in or >> around >>>> there -- the big problem is that debugging it is rather painful since >>> that >>>> logic is in the middle board of a three board set, with jumper blocks >> on >>>> top -- so bringing it out on an extender isn't an option. I'm > curious >> if >>>> anyone's seen this issue or is so very familiar with the logic that > the >>>> fault is obvious. >>>> >>>> I suspected the 7496 shift register at E14 which takes in the > cylinder >>>> address to be compared w/the header on disk, and I went ahead and >>> replaced >>>> it in the hopes that I'd get lucky, but no go. >>>> >>>> Anyone have any advice? >>>> >>>> Thanks, >>>> Josh >>>> >>>> >>> I'll add that during the format/verification the drive seeks properly >> (i.e. >>> it's not missing a step or overstepping), which I've confirmed by >> watching >>> the thing walk through the tracks with the cover off. >>> >>> - Josh >>> >> >> Partitions as rka0 / rka1? >> B >> >>> >> >